1. Field of the Invention
The present invention relates to a silicon-containing polymer and a process for its production. In particular, the invention relates to a silicon-containing polymer that is useful as a primary agent in a resist material composition that provides intricate resist patterns by exposure to radiation with ArF excimer laser light, an electron beam or the like followed by development with an alkali developing solution, and to a process for its production. The invention further relates to a resist composition containing such a polymer, to a method of forming resist patterns using it, and to a method of fabricating electronic devices including LSIs, magnetic heads, liquid crystal devices, MCMs, etc. and photomasks using the method.
2. Description of the Related Art
With the trend toward higher integration and higher functionality of electronic devices, such as semiconductor devices, in recent years, progress continues to be made toward more intricate and multilayered wirings. In the manufacture of second generation semiconductor devices with ever higher integration and higher functionality, research has begun on using ArF excimer lasers and EUV light as exposure light sources in lithography techniques for intricate working, and progress is being made toward shorter wavelength applications. Problems raised with shorter wavelength light sources include the transmittance of the resist materials and reflection from the substrates, but surface imaging has been proposed as an effective technique to counter these problems, and a particularly effective method is the bi-layer resist method employing silicon-containing polymers as resist materials.
According to the bi-layer resist method, an organic resin is coated to a film thickness of 1 xcexcm, for example, to form a lower resist layer on which there is formed an upper resist layer of a thin film of about 0.1-0.2 xcexcm, and then the upper resist layer is first patterned by light exposure and development of the upper layer and the resulting upper layer pattern is used as a mask for etching of the lower layer, to form a resist pattern with a high aspect ratio. The bi-layer resist method can alleviate or prevent the influence of level differences in the substrate and reflection from the substrate surface by the lower layer resist, while the small film thickness of the upper layer resist allows improved resolution compared to single-layer resist methods. Consequently, the bi-layer resist method is more advantageous than the single-layer resist method for formation of intricate patterns on substrates with large level differences and it is therefore believed to be a more effective resist process for the shorter wavelengths of exposure light sources which will be used in the future.
Bi-layer resist materials employing various silicon-containing polymers have been reported to date (for example, Japanese Unexamined Patent Publications SHO No. 58-96654, No. 61-108628, No. 62-104032 and No. 62-220949, Japanese Unexamined Patent Publications HEI No. 1-56732, No. 1-222254, No. 3-29311, No. 5-58446, No. 5-181280, No. 6-95385, No. 6-184311, No. 6-202338 and No. 11-130860), but none of those available have been excellent for alkali development in terms of shelf-life, sensitivity, resolution, O2-RIE resistance, heat resistance, or shorter wavelengths of exposure light sources for pattern intricacy. In particular, none have exhibited excellent developing properties in a 2.38% tetramethylammonium hydroxide (TMAH) aqueous solution, which is currently a commonly used alkali developing solution for mass production of LSIs, and this has been a drawback against their application to general purpose developing equipment.
It is an object of the present invention to overcome the drawbacks of the prior art described above by providing a silicon-containing polymer whose production is simple, which exhibits an excellent shelf-life, which is suitable as a resist material that can be easily developed with common alkali developing solutions, and which simultaneously provides high sensitivity, high resolution, high O2-RIE resistance and high heat resistance.
It is another object of the invention to provide a silicon-containing polymer, a process for its production, a negative non-chemical amplification resist composition or chemical amplification resist composition containing it, a resist pattern-forming method employing the composition, and a fabrication method for electronic devices and photomasks that employs the method.
As a result of much diligent research aimed at achieving the aforementioned object, the present inventors have found that the problems described above can be solved by using a silicon-containing polymer with a specific proportion of functional groups.
Thus, the present invention provides a silicon-containing polymer including the structure represented by formula 1 below as a main structural unit. 
where R1 represents a monovalent organic group, R2 represents a direct bond or a divalent organic group, R3 represents a monovalent organic group or an organosilyl group, any of which groups may be of different types, X represents hydrogen, a monovalent organic group or an organosilyl group, which groups may be of different types, k and l are positive integers, m and n are 0 or positive integers, and these subscripts satisfy the following relationship.   0   less than       1          1      +      m      +      n        ≦      0.8    ⁢          xe2x80x83        ⁢    0    ≦      m          1      +      m         less than   0.2
That is, in formula 1, the ratio of the carboxylic acid group-containing triorganosiloxane portion and the carboxylic acid derivative group-containing triorganosiloxane portion is restricted, as represented by l and m. When a silicon-containing polymer according to the invention having the structure of formula 1 as the main structural unit is used as a negative non-chemical amplification resist, the carboxylic acid group-containing triorganosiloxane portion confers alkali solubility, thus affecting the solubility and resolution in alkali developing solutions, and consequently it must be present in a prescribed amount. Similarly, since the carboxylic acid derivative group-containing triorganosiloxane portion has an adverse effect of lowering the alkali solubility and resist resolution, its content is also restricted. For this reason, the carboxylic acid group-containing triorganosiloxane portion and the carboxylic acid derivative group-containing triorganosiloxane portion are present in a specific proportion represented by the relational equality given above.
The invention also provides a resist composition containing a silicon-containing polymer of the invention having the structure of formula 1 as the main structural unit. The resist composition is primarily a negative non-chemical amplification resist composition. The resist composition may contain one or more different silicon-containing polymers of the invention having the structure of formula 1 as the main structural unit, and if necessary it may also contain other desired polymers or compounds.
The invention also provides a silicon-containing polymer including the structure represented by formula 3 below as a main structural unit. 
where R1 represents a monovalent organic group, R2 represents a direct bond or a divalent organic group, R7 and R8 each independently represent a monovalent organic group or an organosilyl group, any of which groups may be of different types, X represents hydrogen, a monovalent organic group or an organosilyl group, which groups may be of different types, k and q are positive integers, l, n and p are 0 or positive integers, and these subscripts satisfy the following relationship.   0  ≦      l          l      +      n      +      p      +      q         less than       0.5    ⁢          xe2x80x83        ⁢    0.1     less than       q          l      +      n      +      p      +      q        ≦  0.8
That is, in formula 3, the ratio of the carboxylic acid group-containing triorganosiloxane portion and the carboxylic acid derivative group-containing triorganosiloxane portions is restricted, as represented by l, p and q. When a silicon-containing polymer according to the invention having the structure of formula 3 as the main structural unit is used as a positive chemical amplification resist, the carboxylic acid group-containing triorganosiloxane portion exhibits alkali solubility such that the non-exposed sections dissolve during development, and therefore its content is restricted. Similarly, the carboxylic acid derivative group-containing triorganosiloxane portion (q) has a functional group that is eliminated by acid catalysts or when necessary heating, and this elimination reaction occurring at the exposed sections gives a resist pattern. Since the carboxylic acid derivative group-containing triorganosiloxane portion (p) that does not undergo elimination by the action of acid or the like has an adverse effect of lowering the alkali solubility and resist resolution, its content is also restricted. For this reason, the carboxylic acid group-containing triorganosiloxane portion and the two different carboxylic acid derivative group-containing triorganosiloxane portions are present in a specific proportion represented by the relational equality given above.
The invention also provides a resist composition containing a silicon-containing polymer of the invention having the structure of formula 3 as the main structural unit. The resist composition may contain one or more different silicon-containing polymers of the invention having the structure of formula 3 as the main structural unit, and if necessary it may contain an acid generator or if necessary it may also contain other desired polymers or compounds.
The resist composition of the invention may be used either in a single-layer resist method or in a bi-layer resist method.
One resist pattern-forming method according to the invention comprises using a resist composition of the invention to form a resist layer on a working substrate, and forming a resist pattern by light exposure and development of the resist layer.
Another resist pattern-forming method according to the invention is a method of using a first resist material to form a lower resist layer on a working substrate, using a second resist material to form an upper resist layer thereover, patterning the upper resist layer by light exposure and development, and etching the lower resist layer using the resulting upper layer pattern as a mask to form a resist pattern, and it comprises the use of a resist composition according to the invention described above as the second resist material.